When combatants are of elements not next to each other (in the above list), damage is dealt normally.

Hakuoro's ? means he gets no damage bonus to anyone, and is not weak against anyone. The good thing here is that his combo finisher ALWAYS chooses the element the enemy is weak against, so it will always inflict maximum damage.

Enemies without elements deal and receive damage normally. The fact that they deal high damage and receive low damage is purely statistical (i.e. they have high ATK and DEF, as compared to regular units).

Light and Darkness counter each other. That basically means Light > Dark and Dark > Light. Using them against, or them being attacked by, any elements in the normal cycle does not incite any damage bonus or defeciency.